With increasing power of personal computers, a diversity of office machines can be employed with the personal computers to achieve various purposes. The diverse office machines, however, occupy lots of space. A multifunction peripheral having multiple functions in one structural unit, for example the functions of a printer, a scanner, a fax machine and/or a copy machine, is thus developed. As a consequence, the processing capability of the multifunction peripheral is increased and the operative space thereof is reduced.
Nowadays, the printer, a scanner, a fax machine, a copy machine or the multifunction peripheral usually has an automatic document feeder for successively and continuously feeding many paper sheets. After a stack of papers to be scanned are placed on the sheet input tray of the automatic document feeder, the sheet-feeding mechanism of the automatic document feeder will successively transport the paper sheets into the inner portion of the office machine so as to implement associated operations such as scanning, faxing, scanning operations and the like.
Referring to FIG. 1(a), a schematic cross-sectional view of a conventional automatic document feeder for use with an office machine is illustrated. The automatic document feeder 10 of FIG. 1(a) principally includes a pick-up module 11, a transfer module 12, an ejection module 13, a paper input tray 14 and a paper ejecting tray 15. The office machine further includes an image processing module 19 and a glass platform 191 under the automatic document feeder 10.
After a stack of paper sheets 141 to be scanned are placed on the paper input tray 14, the pick-up module 11 may successively pick the uppermost paper sheets one by one into the passageway within the automatic document feeder 10. Next, the paper sheet 141 is transported by the transfer module 12 across the glass platform 191 so that a first side of the paper sheet is scanned by the image processing module 19. The paper sheet 141 whose first side has been scanned is then ejected to the paper ejecting tray 15 by the ejection module 13. For a purpose of performing a duplex scanning operation, the transfer module 12 further includes an inverting member 121 adjacent to the ejection module 13. After the first side of the paper sheet 141 has been scanned and a majority of the paper sheet 141 is ejected to the paper ejecting tray 15, the paper sheet 141 is turned over by the inverting member 121 and then fed into the passageway. Next, the paper sheet 141 is transported by the transfer module 12 across the glass platform 191 so that a second side of the paper sheet is scanned by the image processing module 19.
Please refer to FIG. 1(a) again. The pick-up module 11 includes a pick-up roller 16, a separation roller 17 and a paper stopping module 18 (as is also shown in FIG. 1(b)). The pick-up roller 16 is driven by a driving motor (not shown) to rotate and thus the pick-up roller 16 is either ascended or descended. When the pick-up roller 16 is descended to contact with the paper sheet 141, the paper sheet 141 is fed by the pick-up roller 16. The separation roller 17 is rotated to separate the uppermost paper sheet 141 from the stack of paper sheets, thereby picking a single paper sheet to the transfer module 12.
FIG. 1(b) is a schematic perspective view illustrating a paper stopping module 18 of the automatic document feeder 10. The paper stopping module 18 includes a rotating shaft 181, a clamp element 182 and a paper stopping plate 183. An end of the clamp element 182 is sheathed around the rotating shaft 181 and fixed by a spring 184. The stopping plate 183 is clamped by the other end of the clamp element 182. The rotating shaft 181 is driven by another motor (not shown) to rotate in either a clockwise or anti-clockwise direction. Due to the change of friction force between the rotating shaft 181 and the clamp element 182, the stopping plate 183 is pivotal about the rotating shaft 181. When the stopping plate 183 is rotated to the uppermost position or the lowermost position, idle running of the motor which is connected to the rotating shaft 181 is rendered.
In a case that no paper-feeding instruction is received by the automatic document feeder 10, the pick-up roller 16 is raised to a standby position. Meanwhile, the stopping plate 183 is correspondingly raised such that the paper sheets 141 on the paper input tray 14 are hindered from being transported into the paper feeding port.
Whereas, in a case that a paper-feeding instruction is received by the automatic document feeder 10, the motor which is connected to the rotating shaft 181 exerts a positive driving force on the rotating shaft 181. As a consequence, the rotating shaft 181 is rotated and the stopping plate 183 is rotated downwardly to the lowermost position. Meanwhile, the uppermost paper sheet may be transported into the paper feeding port without being stopped by the stopping plate 183. At that moment, the pick-up roller 16 is driven by the driving motor and lowered to a paper-feeding position where the pick-up roller 16 contacts with the uppermost paper sheet 141. The separation roller 17 is rotated to separate the uppermost paper sheet 141 from the stack of paper sheets, thereby picking a single paper sheet to the transfer module 12.
When a sensor (not shown) of the automatic document feeder 10 detects that the paper sheet 141 reaches the separation roller 17, the rotating shaft 181 is driven by the motor to rotate in a reverse direction and the pick-up roller 16 is raised to the standby position. Meanwhile, the clamp element 182 is also reverse rotated and the stopping plate 183 is correspondingly raised to stop the paper feeding port, thereby preventing the remainder paper sheets from being transported into the paper feeding port. Until the uppermost paper sheet is ejected to the paper ejecting tray 15, the above procedures are repeated to successively feed the remainder paper sheets one by one.
As previously described, after the first side of the paper sheet 141 has been scanned and a majority of the paper sheet 141 is ejected to the paper ejecting tray 15, the paper sheet 141 is turned over by the inverting member 121 and then fed into the passageway. Next, the paper sheet 141 is transported by the transfer module 12 across the glass platform 191 so that a second side of the paper sheet is scanned by the image processing module 19. Conventionally, when the paper sheet 141 is turned over by the inverting member 121 and fed into the passageway, the rotating shaft 181 is driven by the motor to rotate and the stopping plate 183 is rotated downwardly to the lowermost position. As known, the procedure of rotating the stopping plate 183 to the lowermost position is redundant at the moment when the paper sheet 141 is turned over by the inverting member 121 and fed into the passageway, because the paper sheet 141 comes from the paper ejecting tray 15 rather than the paper input tray 14. The frequent idle running of the motor for fixing the stopping plate 183 at the lowermost position may reduce the motor's operating life. Moreover, the use of the motor for driving the rotating shaft 181 increases the fabricating cost. In addition, the performance of stopping the paper sheets by the stopping plate 183 is usually unsatisfied. The rotation of the rotating shaft 181 may result in a drag force between the rotating shaft 181 and the clamp element 182, which increases the burden of the overall system.
In views of the above-described disadvantages resulted from the conventional method, the applicant keeps on carving unflaggingly to develop a paper-feeding mechanism of an automatic document feeder according to the present invention through wholehearted experience and research.